Overshield (D20 Modern Equipment)
From D&D Wiki
When a character with an energy shield touches an overshield, any and all energy shields they possess instantly increase their current HP to three times their max HP. Next round, and all rounds after until the energy shield's hit points are reduced to their normal maximum value or below, the energy shield takes 1 point of damage in addition to any damage it takes from weapon fire, etc. The overshield disappears after it is touched.
An Overshield has a purchase DC of 40, with a restriction of Mil (+3).